The ever increasing density of geostationary satellites demands increasing numbers of antennas for tracking and communication purposes. This situation can be somewhat alleviated by the use of Multibeam Antennas (MBA), whereby one antenna system can be used to receive from, and transmit to, many satellites simultaneously. As satellite antenna systems tend to be large in volumetric size, reduced real estate requirements represent a significant advantage. Each MBA has many feed horns for reception and/or transmission and the number of feed horns determines the number of satellites that can be accessed.
Alignment of a feed horn in single beam axisymmetric antennas can be achieved relatively easily by centralising the feed with respect to the main surface of the antenna and levelling the feed aperture with the antenna pointing to zenith. An example of a single beam antenna is the circularly symmetrical Cassegrain type.
MBAs, like the classical Cassegrain or Gregorian reflectors, typically employ a pair of reflector surfaces, namely a main reflector and a sub-reflector. The shape and size of the reflector surfaces are different, however, and typically a MBA has only one plane of symmetry. Multiple reflections of the beam and the lack of symmetry between the reflecting surfaces demand an alternative and more complex method of aligning the feed horns than is necessary in the case of a single beam axisymmetric antenna. Accurate alignment of each feed horn is necessary to prevent or reduce interference between adjacent beams.
Consequently, a need exists for a method and apparatus for the alignment of one or more feed horns in a multibeam antenna system.